This invention relates to independent focus compensation for multi-axis imaging systems, and particularly to independent focus compensation for microscope arrays.
In a multi-axis imaging system, as that term is used herein, a plurality of optical elements are arranged in an array so as to have a fixed relationship to one another. One advantage of such a system is that all of the elements of the array may be moved in unison to scan an object so as to bring respective images of the object into focus at a desired image plane. In particular, in a miniature microscope array a plurality of miniature microscope objectives arranged in an array is employed instead of a single objective to scan a large field of the object more rapidly at high resolution than can be achieved with a single objective. Such a miniature microscope array is disclosed in PCT Patent Publication No. WO 02/075370, published Sep. 26, 2002. Where used to image a common specimen, a miniature microscope array is also referred to as an array microscope.
In a microscope array, the image sensors for each element of the array are preferably disposed on a single, substantially flat substrate so as to facilitate fabrication, assembly, and electrical connection. In that case, the axial positions of the sensors corresponding to each microscope element cannot be adjusted independently. However, fabrication and assembly errors in the optics will cause the positions of respective image planes of individual microscope elements of a microscope array to vary so as not to be substantially coplanar. In that case, where the respective object planes of the microscope elements are substantially coplanar, some of the images will not be co-planar with their respective image sensors, so the respective image sensors will detect a sub-optimally focused image. In principle, this problem may arise in any multi-axis imaging system having an array of sensors and corresponding optical elements. To avoid this problem, the lens surface shapes, lens thickness and lens separations of each element require extremely tight tolerances. However, such tolerances are difficult and expensive to achieve.
Accordingly, it would be desirable to have some means to compensate for differences in image plane position among the individual elements of a multi-axis imaging system, particularly an array microscope, so as to facilitate fabrication of such systems and ensure optimal focus of the images of all of the individual array elements.